Smoke Extraction Research Articles

Optimisation of smoke extraction system in fire scenarios using CFD modelling

Understanding the consequences of fuel release and fire accident is an important aspect of the design and construction of buildings and infrastructures. Particularly, an increasing number of catastrophic consequences of recent fire accidents in high-rise buildings has led to the demand for a rigorous and holistic approach for infrastructure fire safety analysis and performance evaluation. The current study proposes a framework for liquefied petroleum gas heat release simulations and modelling the visibility of evacuees on the egress path during a fire event using efficient computational fluid dynamics (CFD) model. The framework consists of scenario modelling, optimised smoke detector layout, mechanical smoke extraction system, and visibility analysis. The CFD simulation is first validated using experimental data demonstrating a very good agreement. A case study for detector layout is then considered, showing the proposed approach increases the visibility of the egress path along the corridor of a building during fuel release and fire accident. The study will offer an effective platform for modelling fire risk and assessing the performance of fire safety mechanisms in buildings which can be also beneficial to enhance urban infrastructures safety.

Numerical Investigation of Smoke Propagation in Road Tunnels Caused by a Burned Truck

Abstract The efficiency of smoke extraction for longitudinal and transverse tunnel ventilation systems was studied in this paper by conducting numerical simulations using computational fluid dynamics (CFD). The smoke was assumed to result from a fire initiated from a truck inside the tunnel. The most dangerous issue regarding the fire inside tunnels is smoke as it leads to low visibility and choking and may lead to death. The most important result of this paper refers to that the longitudinal ventilation design does not provide efficient smoke extraction compared to the transverse ventilation design as the air jets push the smoke in the downstream direction and then the smoke spreads randomly after the flow loses its momentum gradually. There is a big drop in the visibility for the longitudinal ventilation design that appeared many times and at many locations downstream the fire location. On the other hand, the transverse ventilation design provided more efficient smoke extraction as the jet fan upstream the fire is turned off while the supply fan downstream the fire is reversed to work as an exhaust fan. As a conclusion based on the findings of this paper, it may be said that the transverse ventilation design provided more safe conditions, lower contaminants concentrations, and higher visibility values compared to the longitudinal ventilation design. This work tends to add more information to minimize the research gap related to having a detailed comparison between the two ventilation strategies for a special case where the fire size is relatively large in a long tunnel.

On the Use of Solid Curtains Near Smoke Extraction Vents to Control Smoke Spread Resulting From Fire in Road Tunnels

AbstractThe effectiveness of the smoke control strategy plays an important role in increasing safety levels when fire accidents occur in road tunnels. This paper introduces clarifications about how the efficiency of smoke extraction control using solid curtains can be increased by placing smoke extraction vents close to the solid curtains. The effect of adding a solid curtain with different heights and at various positions relative to a smoke extraction vent was studied in this paper. A 14.3% increase in the vent flowrate occurs at the time corresponding to the fire peak heat release rate when the distance between the solid curtain and the vent is equivalent to 90% of the tunnel height and when the solid curtain height is equal to 16% of the tunnel height. High temperature and low visibility conditions occur near the solid curtain at the smoke-trapped area when the smoke curtain height exceeds 40% of the tunnel height. Using a solid curtain positioned far away from the vent with a distance equals to 90% of the tunnel height and with a height in the range from 16% to 30% of the tunnel height achieves the best results in terms of suppression of smoke spread and attaining acceptable visibility and temperature levels at the region where the smoke is trapped by the solid curtain.

Experimental studies on the smoke extraction and smoke control performance by the ventilation shaft in extra-long road tunnels

Ventilation shaft is widely employed in the extra-long road tunnels in China. For deeper understandings of the smoke extraction and smoke control characteristics of the ventilation shaft, a total of 98 experiments were conducted in a 1/20 model scale tunnel. The effects of heat release rate, board location, and operation frequency were investigated. The results indicate that the mechanical board-coupled shaft (MBCS) can achieve better smoke extraction and smoke control performances than the traditional mechanical ventilation shaft (MTS). Though further research on the MBCS, it can be found that smoke extraction and smoke control performance of the MBCS are highly affected by the board location and operation frequency. Besides, as the power of the fire source increases, the smoke extraction performance of the MBCS increases, but the corresponding smoke control will be more difficult. Moreover, it was found that the optimal operation conditions for the MBCS to achieve the best smoke extraction performance and smoke control performance are different. Therefore, the uniform parameter for characterizing both the smoke extraction performance and the smoke control performance was established. And based on this parameter, the overall performance of the MBCS under different operation conditions can be compared, which may contribute positive significance in the smoke control and extraction design with extra-long road tunnels.

Plug-holing height and complete plug-holing phenomenon in naturally ventilated tunnel fires with vertical shaft

The plug-holing phenomenon in naturally ventilated tunnel fires with vertical shaft has been receiving considerable attention, however, there is still no simple physical quantity to represent the degree of plug-holing. A series of numerical simulations were conducted to analyze the ventilation performance of vertical shaft in tunnel fires by considering different shaft geometries. Plug-holing height and complete plug-holing were proposed to describe the degree of plug-holing. The influences of shaft geometry on smoke extraction efficiency and plug-holing height were likewise analyzed. Results show that the total mass flow rate in the vertical shaft increases with the increase of shaft length and height, and is more sensitive to shaft length. By contrast, the increase in the pure smoke in the shaft is relatively limited. Moreover, the dimensionless plug-holing height is considerably sensitive to and significantly increases with the shaft length. However, the dimensionless plug-holing height has lower sensitivity to the shaft height and shows no evident monotony with a change in shaft height. Accordingly, a prediction model of the dimensionless plug-holing height is eventually established on the bases of simulated data. Critical criteria for determining the occurrence of complete plug-holing in car fire scenarios have been identified and can be described as Ri∗0.09α1.22=5.16.

Effect of lateral concentrated smoke extraction on the smoke back-layering length and critical velocity in a longitudinal ventilation tunnel

In this study, the thermal smoke back-layering behavior and critical ventilation velocity of tunnel fires were investigated experimentally under the combined effect of lateral concentrated smoke extraction and longitudinal ventilation. The smoke back-layering length, critical ventilation velocity, and confinement velocity were analyzed and discussed. The results indicate that the smoke back-layering length decreases with increasing lateral concentrated smoke extraction velocity when the longitudinal ventilation velocity is less than the confinement velocity. However, above the confinement velocity, the smoke back-layering length increases with increasing lateral concentrated smoke extraction velocity. The critical velocity also shows an increasing trend with an increase in the lateral concentrated smoke extraction velocity. Finally, a correlation equation for the critical velocity of tunnel fires under the combined effect of lateral concentrated smoke extraction and longitudinal ventilation was proposed.

Experimental studies on the smoke extraction performance by natural ventilation with a board-coupled shaft in a deep buried tunnel

In theory, if the plug-holing phenomenon can be effectively eliminated, the application of natural ventilation with vertical shaft will no longer be limited to shallow buried tunnels, or even extended to deep buried tunnels. Researches have validated that the board-coupled shaft (BCS) can efficiently eliminate the plug-holing phenomenon and promote the smoke extraction performance in a shallow buried tunnel. The purpose of this paper is to explore whether the BCS is effective and has stable smoke extraction performance in deep buried tunnels. Experiments were conducted in a 1/20 scale model tunnel, and the height of the board-coupled shaft applied in this study is 5 times the height of the tunnel height. The influence of heat release rate (HRR) and board location on the smoke extraction performance was investigated. Experimental results indicated that the BCS is effective and has stable smoke extraction performance for the deep buried tunnel applied in this study. Besides, it can be found that the smoke extraction efficiency of the BCS will be improved and the improvement in the smoke extraction performance with BCS is stable when the power of the fire source increases. Also, the optimal board location for the BCS to achieve the peak smoke extraction performance was obtained and the peak smoke extraction performance of the BCS is about 1.451–1.457 times of the traditional shaft. Beyond that, two dimensionless correlations were developed under the general condition that the first shaft cannot extract the entirety of the smoke, one is the correlation function for analyzing the smoke temperature difference and the CO concentration in the shaft; the other is the correlation for predicting the dimensionless volume flow rate under different HRRs and board locations. These studies may contribute positive significance for promoting the application of natural ventilation with vertical shafts.

The Design of the Control System of Fire Control and Smoke Extraction Robot Based on PLC

The purpose of this paper is to design a plc-based control system of fire control and smoke extraction robot, which can realize the purpose of water cannon, vehicle body movement and non-line-of-sight operation. This control system is mainly composed of PLC control system, video system, remote control system, motor drive system. PLC Through CANopen message transmission protocol, the function of distributed control system is realized. The main task is to receive the CAN command of remote control, so as to realize the command control of vehicle body action (multi-way valve), yuntai action and water cannon action. The design meets the design requirements, has good operability and reliability, in the industry has a certain promotion significance.

Experimental study on the effect of lateral concentrated smoke extraction on smoke stratification in the longitudinal ventilated tunnel

SummarySmoke is the main cause of death in tunnel fires. It is one of the important measures to maintain smoke stratification in the early stage of tunnel fire. This article focused on experimentally studying the combined effect of lateral concentrated smoke extraction and longitudinal ventilation on the smoke stratification, which never be revealed before. The velocity of the smoke layer and air layer, vertical temperature distribution, and the flow patterns of the smoke were measured. It was found that the longitudinal ventilation and lateral concentrated smoke extraction would affect the flow of the smoke and change the shear velocity between the smoke layer and air layer, then, the patterns of the smoke layer will be affected. And the flow patterns with Froude (Fr) number can be classified into three categories: (a)Fr < 0.6, with stable smoke stratification; (b) 0.6 < Fr < 0.85, with a stable smoke stratification but the blurring interface; and (c) Fr > 0.85, the smoke layer is completely unstable. The result can provide a reference for ventilation design of immersed tube tunnels.

Numerical investigation on the effect of ambient pressure on mechanical smoke extraction efficiency in tunnel fires

This paper has analyzed the ambient pressure on the effect of the efficiency of the mechanical smoke extraction system in tunnel fires. These were simulated by Large Eddy Simulation (LES) with Fire Dynamics Simulator (FDS). The simulation results indicate that it is not the instance that the higher the exhaust rate, the better the smoke exhaust efficiency of the exhaust vent. There is a critical exhaust rate at which excessive fresh air entrainment, such as plug-holing of the smoke layer, can be avoided. The mechanical smoke exhausting process is affected by two competitive forces: horizontal inertial force and vertical suction force. The thickness and horizontal velocity of the thermal smoke layer in the tunnel increase as the ambient pressure decreases. At this time, the vertical suction force required for the occurrence of the plug-holing phenomenon increases, and thus the critical exhaust rate increases. A linear relationship between the dimensionless critical exhaust rate Vcri∗ and the modified heat release rate Q˙∗ was proposed to characterize the influence of ambient pressure on the mechanical smoke exhaust efficiency. When the exhaust rate is 0.5 times the critical exhaust rate, the smoke mass fraction exhausted from the exhaust vent (E) reaches the maximum value.

Numerical study on the smoke extraction efficiency and the improvement through a smoke reservoir in the naturally ventilated tunnel with vertical shaft

Plug-holing of the smoke layer is an unfavorable phenomenon for the smoke extraction efficiency in the naturally ventilated tunnel with vertical shaft. In this work, theoretical analysis and large eddy simulation (LES) are carried out to investigate how to prevent the occurrence of the plug-holing phenomenon and improve smoke extraction efficiency. The results show that the occurrence of plug-holing is influenced by the height, cross-sectional area and total pressure loss coefficient of the vertical shaft, as well as the thickness of the smoke layer. A modified dimensionless number Fr* is proposed to represent the proportion of smoke in the exhausted mass flow. Fr* varies as the −1/4 power of the cross-sectional area of the shaft, −1/2 power of the height of the shaft, and increases linearly with the thickness of the smoke layer. The critical value of Fr* for predicting whether the plug-holing phenomenon occurs is determined to be 0.34 by combining the results of the previous small-scale experiment. In addition, a smoke reservoir is designed under the shaft to increase the thickness of the smoke layer, which is proven to be effective in preventing the occurrence of the plug-holing phenomenon and improving the smoke extraction efficiency of the vertical shaft. The findings of this paper contribute to the understandings of smoke extraction for naturally ventilated tunnel with vertical shaft, and the results are also useful to the fire protection engineering in tunnels.

Impacts of longitudinal air velocity and fuel flow rate on flame radiative fraction in tunnel

Fires in tunnels have attracted special attention in recent years due to catastrophic fires, which cause huge human and economic losses. For accurate fire modelling and ventilation system design, it is critical to understand the correct radiative fraction (Xr) of the flame. Recent study has proved that Xr decreases with the increase of longitudinal air velocity in heptane pool fires. However, the impacts of longitudinal air velocity and fuel flow rate on Xr in propane or liquefied petroleum gas tunnel fires have not been studied. To fill the gap, this paper conducts two sets of fire experiments in a 1/20 reduced-scale wind tunnel using a porous burner. Unique visible flame shapes are observed and described by the ‘back-to-back conical frustum’. The geometric parameters and their variations with the momentum flux ratio are discussed. In comparison with the experimental results, the radiation model using the proposed flame shape shows an 80 % accuracy. The predictive radiative fractions of the two tests are calculated and compared with other tests from literature. The coupling effects of longitudinal air velocity and fuel flow rate on the flame radiative fraction are studied in detail. And their influences on key parameters of smoke extraction system are analyzed.

Increasing energy efficiency and resource saving thanks to the design solution on the use of reversible jet ventilation system for four-storied underground garage in national cultural center of Kazan

In modern metropolitan cities, mass construction of multi-storied underground and closed-type above-ground garages of quite large areas with quite low ceilings (up to 3.5 - 2.5 m) is observed, which requires new approaches to the selection of the ventilation arrangement and its main technical characteristics. Jet ventilation systems have found extensive use. In 2018 in Kazan, an underground four-storied garage equipped with reversible jet ventilation and smoke extraction system (the first in Russia) was constructed and handed over to the customer. Taking into account the absence of any experience in Russia in the field of design and construction of jet ventilation systems, a comparative analysis of traditional duct ventilation systems and jet ventilation systems of closed (underground) car-parking spaces widely used all over the world has been performed. The choice of reversible jet ventilation is justified keeping in mind the parameters of energy efficiency and underground space development effectiveness. In this work, we have performed a critical analysis of ventilation systems with regard exactly to these parameters. Besides, we have shown the advantage of reversible jet ventilation in terms of ensuring safe evacuation of people in the case of fire. For the first time, we propose a scientifically grounded method of calculation of longitudinal jet ventilation and smoke removal system of the parking lot. As a result, design rules have been developed to ensure human safety in case of fire and energy efficiency in normal operation of the jet ventilation system.

Influence of multisource fire on temperature distribution and natural smoke exhaust effect in urban tunnels with a shaft

SummaryThe combustion characteristics of multisource fire and single‐source fire are quite different, and there is little research on the influence of multisource fire on the natural smoke extraction effect of shaft in urban tunnels. Therefore, in this article, the method of numerical simulation was used to study the influence of fire power and distance between two fire sources on the natural smoke extraction effect of shaft and the temperature distribution in tunnel in the case of multisource fire. Typical characteristics of smoke are analyzed, such as mass flow rate, temperature distribution, velocity vector, and CO concentration. The simulation results show that when there is a certain distance between the fire sources, the two flames are inclined and close to each other. The smoke temperature under the ceiling is higher under multiple fire sources than that under single fire source. In addition, when one of the fire sources is located at the downstream of the shaft, the smoke emission in the shaft is relatively high. As the distance between fire sources continues to increase, the smoke exhaust rate basically remains stable, and an empirical relationship between smoke exhaust rate and fire source location is established.

Science Mapping of Tunnel Fires: A Scientometric Analysis-Based Study

The topic of tunnel fire attracted considerable attention in past two decades. The popularity of this topic is mainly attributed to the widespread construction of long-span tunnels and their incident fire safety issues, as well as the frequent occurrence of catastrophic tunnel fires. To date, a number of research papers have been published focusing on specific aspects of tunnel fires such as fire dynamics, smoke extraction, fire suppression system, personnel evacuation, fire risk evaluation, and some others with broader areas of focus. In this work, a thorough bibliometric and network analysis is conducted on the basis of peer-reviewed publications on tunnel fires, seeking to provide insights in this topic. A total of 519 research articles are obtained from the Web of Science Core Collection database. It is identified that the most prolific journal is Tunnelling and Underground Space Technology, with 121 papers, accounting for 23.3% of the total. England is the most influential region with the highest citations per document, while China is the most prolific country with nearly a half of the total, where the University of Science and Technology of China is the primary contributor. The visualization and cluster analysis of research topics indicate that the currently bursting topics mainly concentrate on the smoke thermodynamics and smoke extraction based on model-scale tests. The reference analysis and co-citation network also confirm the findings.

ЕКСПЕРИМЕНТАЛЬНІ МЕТОДИ ОЦІНЮВАННЯ ЕФЕКТИВНОСТІ ЗАСТОСУВАННЯ ПЕРЕНОСНИХ ЗАСОБІВ ДИМО- ТА ТЕПЛОВИДАЛЕННЯ

Наведено результати експериментальних досліджень з визначення коефіцієнту ефективного зменшення задимленості і коефіцієнту ефективного зниження температури під час реалізації трьох варіантів нормалізації газоповітряного середовища у випробувальному боксі, а саме під час створення задимленого та високотемпературного середовища та подальшого самостійного зменшення задимленості і зниження температури, під час димо та тепловидалення шляхом нагнітання повітря та шляхом одночасного подавання повітря та розпиленого струменя води до випробувального боксу за допомогою переносного засобу димо- та тепловидалення

Experimental study on the effect of ceiling mechanical smoke extraction system on transverse temperature decay induced by ceiling jet in the tunnel

This paper focused on studying the transverse temperature distributions induced by ceiling jet under the effect of ceiling mechanical smoke extraction system. Many test conditions were investigated by conducted reduced tunnel model experiments. These changes in fire heat release rates (HRRs) and ceiling mechanical smoke extraction velocities were all taken into consideration. The longitudinal and transverse temperature distributions beneath the ceiling were also compared in this paper, it was found that the transverse temperature decays more slowly than the longitudinal temperature without ceiling extraction. In order to reveal the effect of ceiling mechanical smoke extraction system on the transverse temperature distributions induced by ceiling jet in a tunnel, the attenuation rate of transverse temperature increases as the increasing ceiling mechanical smoke extraction velocities. The modified model for transverse temperature attenuation under the ceiling induced by tunnel fire with different ceiling mechanical smoke extraction velocities was developed by modified the characteristic radius. And the dimensionless transverse temperature decay mainly shows a piecewise function.

A simplified mathematical model for estimating gas temperature and velocity under natural smoke exhaust in sloping city tunnel fires

In the previous study, the prediction of gas temperature and velocity in the naturally-ventilated inclined tunnels under traffic blockage has been well concerned (Y. Zhou et al., Sustain. Cities Soc. 45, 2019, 258–270). In this paper, we continue to pay attention to the estimation of internal gas temperature and velocity under natural smoke extraction in both single-slope and gable-slope tunnel fires, a more hazardous scenario. A series of simplified mathematical models based on the equations of continuity, energy and pressure balance was proposed to estimate the gas temperature and velocity in sloping tunnel fires, in which the influences of fire source location, tunnel slope and tunnel geometry were taken into account. In addition, corresponding numerical simulations based on full-size tilted urban tunnel fires were performed using Computational Fluid Dynamics (CFD) method. The results show that the variation trends between CFD and analytical results are basically the same, and the iterative values of gas temperature and velocity coincide well with the simulations. A fast and convenient method for the estimation of gas temperature and velocity in sloping tunnel fires has been proposed, and the results of this work can provide a reference for the optimal design and management of natural smoke extraction systems, and help to ensure the fire safety of single-slope and gable-slope city tunnels.

Surgical Smoke-Hazard Perceptions and Protective Measures in German Operating Rooms.

(1) Background: Hazardous substances in surgical smoke that is generated during laser or electrosurgery pose a potential health hazard. In Germany, the Technical Rules for Hazardous Substances (TRGS 525) have included recommendations for appropriate protective measures since 2014. Up to now, no empirical data has been available on the extent to which recommendations have been implemented in practice. (2) Methods: In 2018, 7089 surgeons in hospitals and outpatient practices were invited by email to participate in an online survey. In addition, 219 technical assistants were interviewed. The questionnaire dealt with knowledge of, and attitudes toward, the hazard potential of surgical smoke, as well as the availability and actual use of protective measures. Furthermore, manufacturers and distributors of smoke extraction devices were asked to give their assessment of the development of prevention in recent years. (3) Results: The survey response rate was 5% (surgeons) and 65% (technical assistant staff). Half of all surgeons assumed that there were high health hazards of surgical smoke without taking protective measures. Operating room nurses were more often concerned (88%). Only a few felt properly informed about the topic. The TRGS recommendations had been read by a minority of the respondents. In total, 52% of hospital respondents and 65% of the respondents in outpatient facilities reported any type of special suction system to capture surgical smoke. One-fifth of respondents from hospitals reported that technical measures had improved since the introduction of the TRGS 525. Fifty-one percent of the surgeons in hospitals and 70% of the surgeons in outpatient facilities “mostly” or “always” paid attention to avoiding surgical smoke. The most important reason for non-compliance with recommendations was a lack of problem awareness or thoughtlessness. Twelve industrial interviewees who assessed the situation and the development of prevention in practice largely confirmed the prevention gaps observed; only slight developments were observed in recent years. (4) Conclusions: The low response rate among surgeons and the survey results both indicate a major lack of interest and knowledge. Among other measures, team interventions with advanced training are needed in the future.

Innovations for smoke management in passenger trains

Spanish manufacturer Construcciones y Auxiliar de Ferrocarriles developed an innovative alternative for compartmentation, based on a smoke extraction system, to guarantee safe conditions during evacuation processes in a passenger unit. To demonstrate its performance in a train unit, a real-scale experimental programme, supported by the application of fire computer modelling, was applied in a new Construcciones y Auxiliar de Ferrocarriles’ rolling stock. The new smoke exhaust system aims to extract the smoke generated during a fire in the passenger area by exhaust fans of the heating, ventilation, and air conditioning system, allowing the ingress of fresh exterior air in the lower part of the rear ends of the car. These key elements create an air flow that evacuates the smoke to prevent people from being exposed to it. Full-scale fire tests were developed in the train unit following the Australian standard AS 4391-1999. A fire of 140 kW was used, and the smoke was generated by a clean smoke machine. Measurement points included six thermocouple trees, 10 gas flow velocity probes and two GoPro HD video cameras (for the estimation of the visibility). The system performance was successful with the tenability criteria, since the value of visibility at the non-fire car was greater than 30 m and the temperature was lower than 30°C during all the tests at a height of 1.7 m above the floor. Experimental results were used to validate the computational model. The computational model results show a good accuracy compared with the tests.